Various AC frequency conversion techniques are known, as well as various phase conversion techniques. The present invention provides a particularly simple combination of both frequency and phase conversion.
One known frequency conversion technique is the inverter-converter approach which rectifies the AC current through a diode rectifier bridge or the like, and smoothes the rectified AC to level DC by means of a capacitor or the like. This level DC is then synthesized into a series of incremental steps to approximate a given sine wave voltage of desired frequency, for example "Power Transistor Applications for Switching Regulators and Motor Control", Marvin W. Smith, General Electric Company Semiconductor Products Department, Auburn, N.Y., October, 1979, Pages 22-23.
The present invention provides in combination a system having a plurality of coordinated but irregular sets of switching times performing in coordination the functions of rectification, frequency change, and single to multiphase conversion, directly from the AC line, without the diode bridge and without the DC filtering and DC synthesization.